JP6603294B2 - Motor driving device and measuring method - Google Patents

Description

  The present invention relates to a motor driving apparatus and a measuring method for driving a plurality of motors and measuring the insulation resistance of the plurality of motors.

  Patent Document 1 shown below discloses a motor drive device that can measure the insulation resistance of a motor without being affected by a leakage current flowing through a semiconductor switching element of an inverter unit.

Japanese Patent Laying-Open No. 2015-169479

  Here, in order to measure the insulation resistance (parasitic resistance) of the motor, it is necessary to wait until the current flowing through the insulation resistance converges. Since the waiting time required for convergence varies depending on the size of the parasitic capacitance of the motor and the like, the waiting time is set to a sufficiently long time determined in advance. However, if the waiting time is set uniformly as described above, there is a problem that the parasitic capacitance of the motor is small, and the measurement time is unnecessarily prolonged even when the convergence is made in a short time.

  Therefore, an object of the present invention is to provide a motor drive device and a measurement method that reduce the time required for measuring the insulation resistance of a motor.

  A first aspect of the present invention is a motor drive device that drives a plurality of motors, and includes a rectifier circuit that rectifies an AC voltage supplied from an AC power supply via a first switch into a DC voltage, and the rectifier circuit. A capacitor that smoothes the rectified DC voltage, a semiconductor switching element of an upper arm that connects the positive terminal of the capacitor and the motor coil of the motor, a negative terminal of the capacitor and the motor coil A lower arm semiconductor switching element to be connected, and by switching operations of the upper arm semiconductor switching element and the lower arm semiconductor switching element, a capacitor voltage of the capacitor is converted into an AC voltage, and a plurality of the motors are A plurality of inverter units to be driven, the positive terminal and the negative terminal of the capacitor A second switch for connecting one of the terminals to the ground, a first detection unit for detecting a ground-to-ground current or a ground-to-ground voltage between the one terminal of the capacitor and the ground, and the capacitor voltage of the capacitor. A second detection unit for detecting, and turning off the semiconductor switching element of the upper arm and the semiconductor switching element of the lower arm of each of the plurality of inverter units to stop the operation of the plurality of motors; Off, the other terminal of the capacitor among the semiconductor switching element of the upper arm and the semiconductor switching element of the lower arm to which the motor coil of the motor to be measured is connected after the second switch is turned on Is turned on, and the motor coil of the motor other than the measurement target is connected. Of the semiconductor switching element of the upper arm and the semiconductor switching element of the lower arm, the one connected to the one terminal of the capacitor is turned on to measure the insulation resistance of the motor to be measured A switch control unit that can be in a measurement state, and in the measurement state, a change amount of the waveform of the ground-to-ground current or the ground-to-ground voltage detected by the first detection unit is calculated, and the change amount is equal to or less than a threshold value A convergence determination unit that determines that the ground-to-ground current or the ground-to-ground voltage has converged, and the ground-to-ground current detected by the first detection unit or the An insulation resistance calculation unit that calculates the insulation resistance of the motor to be measured based on the voltage to ground and the capacitor voltage detected by the second detection unit; Prepare.

  A second aspect of the present invention is a measuring method in which a motor driving device that drives a plurality of motors measures the insulation resistance of the motor, and the motor driving device is supplied from an AC power supply via a first switch. A rectifier circuit for rectifying an AC voltage to be converted into a DC voltage, a capacitor for smoothing the DC voltage rectified by the rectifier circuit, and a semiconductor of an upper arm connecting a positive terminal of the capacitor and a motor coil of the motor A switching element, and a lower arm semiconductor switching element that connects the terminal on the negative electrode side of the capacitor and the motor coil, and by switching operation of the upper arm semiconductor switching element and the lower arm semiconductor switching element, A plurality of inverters for driving a plurality of the motors by converting a capacitor voltage of the capacitor into an AC voltage A second switch that connects one of the positive terminal and the negative terminal of the capacitor to the ground, and a ground-to-ground current or ground between the one terminal of the capacitor and the ground A first detector for detecting an inter-voltage, and a second detector for detecting the capacitor voltage of the capacitor, the semiconductor switching element of the upper arm and the semiconductor of the lower arm of each of the plurality of inverters The upper arm to which the motor coil of the motor to be measured is connected after the operation of the plurality of motors is stopped by turning off the switching element, the first switch is turned off, and the second switch is turned on. Of the semiconductor switching element and the semiconductor switching element of the lower arm, the one connected to the other terminal of the capacitor The upper arm semiconductor switching element and the lower arm semiconductor switching element to which the motor coil of the motor other than the measurement target is connected are connected to the one terminal of the capacitor. A switch control step for turning on the switch and setting the switch to a measurement state in which the insulation resistance of the motor to be measured can be measured; and the ground-to-ground current detected by the first detection unit or the ground in the measurement state A convergence determination step for calculating a change amount of the waveform of the inter-voltage, and determining that the ground-to-ground current or the ground-to-ground voltage has converged when the change amount is equal to or less than a threshold, and the convergence determination step When it is determined, the current to ground or the voltage to ground detected by the first detector and the controller detected by the second detector And an insulation resistance calculating step of calculating the insulation resistance of the motor to be measured based on the density voltage.

  ADVANTAGE OF THE INVENTION According to this invention, the time concerning the measurement of the insulation resistance of a motor can be shortened, and it can prevent that the time concerning the measurement of insulation resistance becomes unnecessarily long.

It is a figure which shows the structure of the motor drive device in embodiment. It is an equivalent circuit diagram showing connection of the insulation resistance of a motor with an equivalent circuit when a motor drive device is in a measurement preparation state. It is a figure which shows the flow of an electric current when the motor drive device shown in FIG. 1 will be in a measurement state. FIG. 2 is an equivalent circuit diagram showing connection of an insulation resistance of a motor with an equivalent circuit in a measurement state of the motor driving device shown in FIG. 1. It is a wave form diagram which shows an example of the relationship between the voltage between grounds at the time of a measurement state, and time, and is a figure for demonstrating the judgment by the 1st method of a convergence judgment part. It is a wave form diagram which shows an example of the relationship between the voltage between ground at the time of a measurement state, and time, and is a figure for demonstrating the judgment by the 3rd method of a convergence judgment part. It is a wave form diagram which shows an example of the relationship between the voltage between ground at the time of a measurement state, and time, and is a figure for demonstrating the determination by the 4th method of a convergence determination part. It is a flowchart which shows the measurement operation | movement of the insulation resistance by a motor drive device.

  The motor driving device and the measuring method according to the present invention will be described in detail below with reference to the accompanying drawings by listing preferred embodiments.

[Embodiment]
<Overall Configuration of Motor Drive Device 10>
FIG. 1 is a diagram illustrating a configuration of a motor drive device 10 according to an embodiment. The motor driving device 10 drives a plurality of motors M. The motor drive device 10 includes a first switch SW1, a converter unit 14, a plurality of inverter units 16, a second switch SW2, a first detection unit 18, a second detection unit 20, and a control unit 22.

  The first switch SW <b> 1 is a switch for turning on / off the supply of the AC voltage from the AC power supply 12.

  The converter unit 14 converts an AC voltage supplied from the AC power supply 12 through the first switch SW1 into a DC voltage. The converter unit 14 includes a rectifier circuit Re that rectifies the AC voltage of the AC power supply 12 supplied via the first switch SW1 into a DC voltage, and a capacitor Ca that smoothes the DC voltage rectified by the rectifier circuit Re. .

  The plurality of inverter units 16 convert the DC voltage (specifically, the voltage of the capacitor Ca) Vc converted by the converter unit 14 into an AC voltage to drive the plurality of motors M.

  In the present embodiment, in order to simplify the description, the number of motors M is three, and the motor driving apparatus 10 includes three inverter units 16 that drive the three motors M. In order to distinguish the three inverter units 16 from each other, each of the three inverter units 16 may be referred to as 16a, 16b, and 16c. The motor M driven by the inverter unit 16a may be referred to as M1, the motor M driven by the inverter unit 16b may be referred to as M2, and the motor M driven by the inverter unit 16c may be referred to as M3.

  The resistance between the three-phase (UVW) motor coils Cu, Cv, Cw of each of the three motors M (M1 to M3) and the ground is referred to as an insulation resistance (parasitic resistance) Rm. In order to distinguish these three insulation resistances Rm from each other, the insulation resistance Rm between the motor coils Cu, Cv, Cw of the motor M1 and the ground is defined as Rm1, and the motor coils Cu, Cv, Cw of the motor M2 between the ground and the ground. The insulation resistance Rm may be referred to as Rm2, and the insulation resistance Rm between the motor coils Cu, Cv, Cw of the motor M3 and the ground may be referred to as Rm3.

  Since the three inverter units 16 (16a, 16b, 16c) have the same configuration, only the configuration of the inverter unit 16a will be described. The inverter unit 16a includes a plurality of semiconductor switching elements S. In the present embodiment, since the motor M having three-phase (UVW) motor coils Cu, Cv, and Cw is used, the plurality of semiconductor switching elements S include an upper-arm semiconductor switching element Suu and a lower arm corresponding to the U-phase. Semiconductor switching element Sud, upper arm semiconductor switching element Svu and lower arm semiconductor switching element Svd according to V phase, upper arm semiconductor switching element Swu and lower arm semiconductor switching element Swd according to W phase, Have

  The three-phase upper arm semiconductor switching elements Suu, Svu, Swu connect the positive terminal of the capacitor Ca and the three-phase (U, V, W) motor coils Cu, Cv, Cw of the motor M1. The three-phase lower arm semiconductor switching elements Sud, Svd, Swd connect the negative terminal of the capacitor Ca and the three-phase motor coils Cu, Cv, Cw of the motor M1.

  For each phase, the upper arm semiconductor switching element S and the lower arm semiconductor switching element S are connected in series, and the upper arm semiconductor switching element S and the lower arm semiconductor switching element S connected in series are: The capacitor Ca is connected in parallel. Specifically, the U-phase semiconductor switching elements Suu and Sud connected in series are connected in parallel with the capacitor Ca. Similarly, the V-phase semiconductor switching elements Svu and Svd connected in series are connected in parallel with the capacitor Ca, and the W-phase semiconductor switching elements Swu and Swd connected in series are connected in parallel with the capacitor Ca. ing.

  The U-phase motor coil Cu of the motor M1 is connected to the emitter of the upper arm semiconductor switching element Suu and the collector of the lower arm semiconductor switching element Sud. The V-phase motor coil Cv of the motor M1 is connected to the emitter of the upper arm semiconductor switching element Svu and the collector of the lower arm semiconductor switching element Svd. The W-phase motor coil Cw of the motor M1 is connected to the emitter of the upper arm semiconductor switching element Swu and the collector of the lower arm semiconductor switching element Swd.

  The inverter unit 16a performs switching operation (on / off operation) of the three-phase upper arm semiconductor switching elements Suu, Svu, Swu and the three-phase lower arm semiconductor switching elements Sud, Svd, Swd (on / off operation). Hereinafter, this is referred to as a capacitor voltage.) Vc is converted into an AC voltage to drive the motor M1.

  The second switch SW2 is for connecting one terminal of the capacitor Ca (in this embodiment, the terminal on the negative side of the capacitor Ca) to the ground in order to measure the insulation resistance Rm (Rm1, Rm2, Rm3). Switch.

  The first detector 18 is a sensor that detects a voltage Vm between one terminal of the capacitor Ca and the ground (hereinafter referred to as a voltage to ground) when the second switch SW2 is turned on. A detection resistor r1 is connected in series with the second switch SW2 between one terminal (terminal on the negative electrode side) of the capacitor Ca and the ground. The first detection unit 18 detects the voltage Vm to ground by measuring the voltage Vm of the detection resistor r1. Since the resistance value of the detection resistor r1 is known, the first detection unit 18 refers to a current flowing between one terminal of the capacitor Ca and the ground (hereinafter referred to as a ground-to-ground current) from the detected ground-to-ground voltage Vm. ) Im may be detected.

  The second detection unit 20 is a sensor that detects a capacitor voltage Vc between both terminals of the capacitor Ca. A detection resistor r2 is connected in parallel with the capacitor Ca. The second detection unit 20 detects the capacitor voltage Vc by measuring the voltage of the detection resistor r2.

  The control unit 22 controls each unit (the first switch SW1, the second switch SW2, the plurality of semiconductor switching elements S and the like) of the motor driving device 10 to drive the motor M (M1 to M3) and the like. The insulation resistance Rm is measured. The control unit 22 includes a processor such as a CPU and a memory.

  The control unit 22 selects any one of the three motors M (M1 to M3) as a measurement target, and measures the insulation resistance Rm of the selected motor M as the measurement target. Therefore, the insulation resistance Rm (Rm1 to Rm3) of all the motors M (M1 to M3) can be measured by switching the motor M selected as the measurement target.

  The control unit 22 includes a measurement target selection unit 30, a switch control unit 32, a convergence determination unit 34, and an insulation resistance calculation unit 36.

  The measurement target selection unit 30 selects the motor M to be measured. The selection of the motor M to be measured may be random or may be based on a predetermined order. The measurement target selection unit 30 outputs information indicating the selected measurement target motor M to the switch control unit 32.

  The switch control unit 32 controls on / off of each of the first switch SW1, the second switch SW2, and the plurality of semiconductor switching elements S. When measuring the insulation resistance Rm, the switch control unit 32 controls each of the first switch SW1, the second switch SW2, and the plurality of semiconductor switching elements S to determine the motor M selected as the measurement target. A measurement state in which the insulation resistance Rm can be measured is set.

  First, the switch control unit 32 turns off all the plurality of semiconductor switching elements S (Suu, Svu, Suu, Sud, Svd, Swd) of all (three) inverter units 16 (16a to 16c). As a result, the operation of all the motors M (M1 to M3) is stopped.

  Then, the switch control unit 32 turns off the first switch SW1 and turns on the second switch SW2. As a result, the AC voltage from the AC power supply 12 is not supplied to the motor driving device 10, and one terminal of the capacitor Ca (in this embodiment, the terminal on the negative side of the capacitor Ca) is connected to the ground. It becomes a state. Thereby, the motor drive apparatus 10 will be in a measurement preparation state.

  FIG. 2 shows that when the motor drive device 10 is in a measurement preparation state (that is, all the semiconductor switching elements S of all the inverter units 16 are all off, the first switch SW1 is off, and the second switch SW2 is on. FIG. 6 is an equivalent circuit diagram showing the connection of the insulation resistances Rm (Rm1 to Rm3) of the motor M (M1 to M3) in an equivalent circuit.

  Here, RU-IGBT1 shown in FIG. 2 indicates the equivalent insulation resistance of the three semiconductor switching elements Suu, Svu, Swu of the upper arm when the inverter unit 16a is in the off state. RU-IGBT2 represents the equivalent insulation resistance of the three semiconductor switching elements Suu, Svu, and Suu of the upper arm when the inverter unit 16b is in the OFF state. RU-IGBT3 represents the equivalent insulation resistance of the three semiconductor switching elements Suu, Svu, Swu of the upper arm when the inverter unit 16c is in the off state. The equivalent insulation resistances RU-IGBT1, RU-IGBT2, and RU-IGBT3 are applied between the collectors and emitters of the three semiconductor switching elements Suu, Svu, and Suu of the upper arms of the inverter units 16a, 16b, and 16c. Is divided by the leakage current that flows from the collector to the emitter in the off state.

  RD-IGBT1 shown in FIG. 2 shows the equivalent insulation resistance of the three semiconductor switching elements Sud, Svd, Swd of the lower arm when the inverter unit 16a is in the off state. RD-IGBT2 represents the equivalent insulation resistance of the three semiconductor switching elements Sud, Svd, Swd of the lower arm when the inverter unit 16b is in the off state. RD-IGBT3 represents the equivalent insulation resistance of the three semiconductor switching elements Sud, Svd, Swd of the lower arm when the inverter unit 16c is in the off state. The equivalent insulation resistances RD-IGBT1, RD-IGBT2, and RD-IGBT3 are applied between the collectors and emitters of the three semiconductor switching elements Sud, Svd, and Swd of the lower arms of the inverter units 16a, 16b, and 16c. Is divided by the leakage current that flows from the collector to the emitter in the off state.

  When the motor drive device 10 is set in the measurement preparation state, the switch control unit 32 at least drives the measurement target motor M based on information indicating the measurement target motor M selected by the measurement target selection unit 30. The semiconductor switching element S is controlled. Although this control will be specifically described later, briefly, the switch control unit 32 applies the capacitor voltage Vc only to the insulation resistance Rm of the motor M to be measured among the insulation resistances Rm of the three motors M. Is applied (so that the current from the capacitor Ca flows), at least the semiconductor switching element S of the inverter unit 16 that drives the motor M to be measured is controlled.

  Thereby, the motor drive apparatus 10 will be in the measurement state which can measure the insulation resistance Rm of the motor M used as a measuring object. The ground voltage Vm at this time is detected by the first detector 18. Note that the first detection unit 18 may detect the ground current Im. This ground-to-ground current Im is a current that flows through the insulation resistance Rm of the motor M to be measured in the measurement state.

  The convergence determination unit 34 determines whether the ground voltage Vm or the ground current Im has converged based on the ground voltage Vm or the ground current Im detected by the first detection unit 18 in the measurement state. The convergence determination unit 34 will be described in detail later.

  The insulation resistance calculator 36 is based on the ground voltage Vm or the ground current Im detected by the first detector 18, the capacitor voltage Vc detected by the second detector 20, and the detection resistor r1. Is calculated. The insulation resistance calculation unit 36 calculates the insulation resistance Rm after the convergence determination unit 34 determines that the ground voltage Vm or the ground current Im has converged.

<Specific Control of Switch Control Unit 32>
Next, the control of the switch control unit 32 will be described in detail.

  When the motor controller 10 is set in the measurement preparation state, the switch control unit 32 relates to the inverter unit 16 connected to the motor M to be measured selected by the measurement target selection unit 30 among the plurality of semiconductor switching elements S. The at least one semiconductor switching element S connected to the other terminal of the capacitor Ca (a terminal on the opposite side to one terminal of the capacitor Ca connected to the ground via the second switch SW2) is turned on. . Thereby, the motor coils Cu, Cv, Cw of the motor M to be measured have the same potential as the other terminal of the capacitor Ca.

  In the present embodiment, since one terminal of the capacitor Ca is a negative terminal, the switch control unit 32 has a plurality of semiconductor switching elements Suu on the upper arm of the inverter unit 16 connected to the motor M to be measured. , Svu, Swu may be turned on. Therefore, the motor coils Cu, Cv, and Cw of the motor M to be measured have the same potential as the positive terminal of the capacitor Ca. At this time, the semiconductor switching element S to be turned on among the plurality of semiconductor switching elements Suu, Svu, Swu of the upper arm is the semiconductor switching element S in any phase of the U phase, the V phase, and the W phase. Good.

  In the example shown in FIG. 3, when the motor M to be measured is the motor M1, the state where the semiconductor switching element Suu of the upper arm of the U phase of the inverter unit 16a is turned on is shown. By doing in this way, regarding the inverter unit 16a connected to the motor M1 to be measured, the capacitor Ca, the semiconductor switching element S of the upper arm turned on (in the example shown in FIG. 3, the semiconductor switching element Suu). ), A closed circuit is formed via the insulation resistance Rm1 between the motor coils Cu, Cv, Cw of the motor M to be measured and the ground and the detection resistance r1.

  In addition, the switch control unit 32 has one of the capacitors Ca among the plurality of semiconductor switching elements S with respect to the inverter unit 16 connected to the motor M other than the motor M to be measured selected by the measurement target selection unit 30. At least one semiconductor switching element S connected to the terminal (one terminal of the capacitor Ca connected to the ground via the second switch SW2). As a result, the motor coils Cu, Cv, and Cw of the motor M other than the measurement target all have the same potential as that of one terminal of the capacitor Ca.

  In the present embodiment, since one terminal of the capacitor Ca is a negative terminal, the switch control unit 32 includes a plurality of semiconductor switching elements Sud in the lower arm of the inverter unit 16 connected to the motor M other than the measurement target. , Svd, and Swd may be turned on. Therefore, the motor coils Cu, Cv, and Cw of the motor M other than the measurement target have the same potential as the terminal on the negative electrode side of the capacitor Ca. At this time, among the plurality of semiconductor switching elements Sud, Svd, Swd of the lower arm, the semiconductor switching element S to be turned on is the semiconductor switching element S in any phase of the U phase, the V phase, and the W phase. Good.

  In the example shown in FIG. 3, the semiconductor switching element Svd of the lower arm of the V phase of the inverter unit 16b is turned on, and the semiconductor switching element Swd of the lower arm of the W phase of the inverter unit 16c is turned on. . By doing in this way, the unnecessary electric current which flows into detection resistance r1 via motors M2 and M3 other than a measuring object can be eliminated.

  FIG. 4 is an equivalent circuit diagram shown in FIG. 2, in which the semiconductor switching element S of the upper arm of the inverter unit 16a that drives the motor M1 to be measured is turned on, and the inverter unit 16b that drives the motors M2 and M3 other than the measurement target. 16c is an equivalent circuit diagram showing a state when the semiconductor switching element S of the lower arm is turned on.

  4 shows an equivalent insulation resistance RU-IGBT1 of the upper arm of the inverter unit 16a in FIG. 2, an equivalent insulation resistance RD-IGBT2 of the lower arm of the inverter unit 16b, and an equivalent insulation resistance RD-IGBT3 of the lower arm of the inverter unit 16c. Is a shorted equivalent circuit diagram. As is apparent from FIG. 4, the equivalent insulation resistance RD-IGBT1 of the lower arm of the inverter unit 16a, the equivalent insulation resistance RU-IGBT2 of the upper arm of the inverter unit 16b, and the equivalent insulation resistance RU- of the upper arm of the inverter unit 16c. The IGBT 3 is connected to the positive terminal and the negative terminal of the capacitor Ca. Therefore, the leakage current flowing through these equivalent insulation resistances RD-IGBT1, RU-IGBT2, and RU-IGBT3 only flows from the positive electrode side terminal of the capacitor Ca to the negative electrode side terminal. Does not flow. Therefore, it can be seen that there is no influence on the measurement of the insulation resistance Rm1 of the motor M1 to be measured. That is, it can be considered that the equivalent insulation resistance RD-IGBT1, RU-IGBT2, and RU-IGBT3 are not present in the measurement of the insulation resistance Rm1.

  Further, the insulation resistances Rm2 and Rm3 of the motors M2 and M3 other than the measurement target are in a state of being connected in parallel with the first detection unit 18. However, if the resistance value of the detection resistor r1 is sufficiently smaller than the insulation resistances Rm2 and Rm3, the influence on the voltage detection and current detection can be ignored. Therefore, the measurement of the insulation resistance Rm1 can be regarded as the absence of the insulation resistances Rm2 and Rm3 of the motors M2 and M3 other than the measurement target. It should be noted that measurement is performed with all lower-arm semiconductor switching elements S turned off, and Rm2 is measured using the resistance value when all the motors M (M1 to M3) have the insulation resistances Rm (Rm1 to Rm3) in parallel. , The influence of Rm3 may be corrected.

  Therefore, the calculation accuracy of the insulation resistance Rm of the motor M to be measured by the insulation resistance calculation unit 36 is improved.

<Specific Determination Processing of the Convergence Determination Unit 34>
Next, the convergence determination unit 34 will be described in detail. The convergence determination unit 34 calculates the amount of change in the waveform of the ground-to-ground voltage Vm or the ground-to-ground current Im detected by the first detection unit 18, and when the amount of change is equal to or less than the threshold value TH, It is determined that the intercurrent current Im has converged.

  The concept is the same whether the voltage Vm to ground or the current Im to ground is used for the determination of convergence. Therefore, the case where the convergence is determined using the voltage Vm to the ground will be described below as an example. .

  FIG. 5 is a waveform diagram showing an example of the relationship between the ground voltage Vm detected by the first detector 18 and time. In a measurement state in which the insulation resistance Rm of the motor M to be measured is measured, the ground voltage Vm decreases with the passage of time after the voltage of the capacitor Ca is applied to the detection resistor r1, and finally there is Nearly converges to the value.

  Specifically, the convergence determination unit 34 determines whether or not the ground-to-ground voltage Vm has converged using any one of a plurality of methods as described below.

<First method>
In the first method, the convergence determination unit 34 uses the absolute value ΔC of the amount (voltage change amount) of the change in the ground voltage Vm during the predetermined time Δt as the change amount of the waveform of the ground voltage Vm. In this case, the convergence determination unit 34 calculates the change amount ΔC from the ground voltage Vm detected by the first detection unit 18 at predetermined time intervals Δt, and determines whether or not the change amount ΔC has become equal to or less than the threshold value TH. to decide.

In the example shown in FIG. 5, the time interval between timings t _{1 to} t ₂ , timings t _{2 to} t ₃ , and timings t _{3 to} t ₄ is a predetermined time Δt. The amount of change ΔC at timings t _{1 to} t ₂ is ΔC ₁ . Moreover, the variation [Delta] C at the timing t ₂ ~t ₃ and [Delta] C _2, the amount of change [Delta] C at the timing t ₃ ~t ₄ and [Delta] C _3. In the example shown in FIG. 5, since the change amount ΔC ₃ in which the ground-to-ground voltage Vm has changed between the timings t _{3 and} t ₄ is equal to or less than the threshold value TH, the convergence determination unit 34 determines the ground-to-ground voltage at the timing t _4. It can be determined that Vm has converged.

  In the example shown in FIG. 5, the predetermined time Δt is set to a fixed time, but the value of the predetermined time Δt may be increased as time elapses. The reason is that the amount of change ΔC in the waveform of the ground voltage Vm decreases with time, so if the predetermined time Δt is set to a certain time, the S / N ratio increases and the determination accuracy may be reduced. Because there is. Further, the threshold value TH may be increased according to the length of the predetermined time Δt.

<Second method>
In the second method, the convergence determination unit 34 uses ΔC / Δt as the amount of change in the waveform of the ground voltage Vm when the absolute value of the amount of change in the ground voltage Vm during the predetermined time Δt is ΔC. Used as In this case, the convergence determination unit 34 calculates the change amount ΔC / Δt from the ground voltage Vm detected by the first detection unit 18 at a predetermined time Δt interval, and the change amount ΔC / Δt is equal to or less than the threshold value TH. Determine whether or not. Similarly, the second method, assuming that the amount of change [Delta] C / Delta] t to ground voltage Vm is varied between the timing t ₃ ~t ₄ becomes equal to or less than the threshold TH, the convergence determination unit 34, the point of timing t ₄ Thus, it is determined that the ground voltage Vm has converged.

  Note that, as in the first method, the value of the predetermined time Δt may be increased with the passage of time.

<Third method>
In the third method, the convergence determining unit 34 obtains a differential value (slope of tangent to the waveform) Dv of the waveform of the ground voltage Vm, and uses the absolute value (the absolute value of the slope) ΔC of the differential value Dv as the amount of change. Use. In this case, the convergence determination unit 34 obtains the differential value Dv from the ground voltage Vm detected by the first detection unit 18, and determines whether or not the absolute value ΔC of the differential value Dv is equal to or less than the threshold value TH.

Figure 6 is a diagram illustrating a differential value at each detection timing t ₁ ~t ₄ of ground voltage Vm (slope) Dv ₁ ~Dv _4. Dv ₁ detected differential value at the timing t ₁ (gradient) Dv, detecting Dv ₂ a differential value Dv at the timing t _2, the detection timing t Dv ₃ a differential value Dv of _3, Dv the differential value Dv at the detection timing t _{4 4} And As shown in FIG. 6, the magnitude (absolute value ΔC) of the differential value (slope) Dv gradually decreases with time (that is, as it converges). In the example shown in FIG. 6, the absolute value ΔC differential value Dv ₄ is equal to or less than the threshold value TH at the detection timing t _4, the convergence determination unit 34 determines that the ground voltage Vm converges at the detection timing t ₄ can do.

<Fourth method>
In the fourth method, when the ground-to-ground voltage Vm has not changed by the reference change amount ΔCs even after the predetermined time T has elapsed, the convergence determination unit 34 determines that the amount of change in the waveform of the ground-to-ground voltage Vm is equal to or less than the threshold value TH. It is determined that the ground voltage Vm has converged. As shown in FIG. 5, the ground voltage Vm gradually decreases with the passage of time. Therefore, as shown in FIG. 7, the time required for the ground voltage Vm to change by the reference change amount ΔCs is It becomes long with progress.

In the example shown in FIG. 7, timings t _{1 to} t ₂ , timings t _{2 to} t ₃ , and timings t _{3 to} t ₄ indicate times when the ground-to-ground voltage Vm changes by the reference change amount ΔCs. For example, the timing t ₂ is a timing at which the ground voltage Vm has changed from the ground voltage Vm at the timing t _{1 by} the reference change amount ΔCs, and the timing t ₃ is from the ground voltage Vm at the timing t _2. This is the timing when the voltage Vm to ground changes by the reference change amount ΔCs. In the example shown in FIG. 7, since the ground voltage Vm from ground voltage Vm by a predetermined time T has passed when time t ₄ does not change the reference change amount ΔCs above, the convergence determination unit 34, a timing t ₄ at timing t ₅ after a predetermined time T has elapsed since, it is determined that the ground voltage Vm converges.

  Thus, in this embodiment, it is determined whether or not the ground-to-ground voltage Vm has converged, and if it is determined that the to-ground voltage Vm has converged, the insulation resistance Rm is measured. The waiting time until the resistance Rm is measured can be shortened. Therefore, the time required for measuring the insulation resistance Rm of the motor M can be shortened.

  The ground-to-earth current Im is obtained by dividing the ground-to-ground voltage Vm by the detection resistance r1, and the detection resistance r1 has a known constant resistance value determined in advance. Therefore, if the above-described ground-to-ground voltage Vm is replaced with the detection resistor r1 × the ground-to-ground current Im, it is possible to determine convergence using the ground-to-ground current Im.

<Operation of Motor Drive Device 10>
Next, the measurement operation of the insulation resistance Rm by the motor driving device 10 will be described according to the flowchart shown in FIG. In step S1, the switch control unit 32 turns off all the semiconductor switching elements S (Suu, Svu, Suu, Sud, Svd, Swd) of all the inverter units 16 (16a, 16b, 16c). Thereby, the driving | operation of all the motors M (M1-M3) stops.

  Next, in step S2, the switch control unit 32 turns off the first switch SW1. Thereby, the supply of AC voltage from AC power supply 12 to motor drive device 10 is interrupted.

  Next, in step S3, the switch control unit 32 turns on the second switch SW2. Thereby, the terminal (one terminal) on the negative electrode side of the capacitor Ca is connected to the ground. As a result, the motor drive device 10 is in a measurement preparation state, and the equivalent circuit at this time is in the state shown in FIG.

  Next, in step S4, the measurement target selection unit 30 selects any one of the plurality of motors M (M1 to M3) as a measurement target. At this time, the measurement target selection unit 30 selects, as the measurement target, the motor M that has not yet been selected as the measurement target.

  Next, in step S5, the switch control unit 32 controls the semiconductor switching elements S of the plurality of inverter units 16 (16a, 16b, 16c), so that the insulation resistance Rm of the motor M to be measured selected in step S4. To a measurement state that can be measured.

  Specifically, for the inverter unit 16 connected to the measurement target motor M, the switch control unit 32 sets the upper arm semiconductor switching element S connected to the positive terminal (the other terminal) of the capacitor Ca. turn on. Further, the switch control unit 32 turns on the semiconductor switching element S of the lower arm connected to the negative terminal (one terminal) of the capacitor Ca for the inverter unit 16 connected to the motor M other than the measurement target. To do. Thereby, for example, when the motor M to be measured is the motor M1, the equivalent circuit shown in FIG. 2 is in the state shown in FIG. Therefore, the current from the capacitor Ca flows through the insulation resistance Rm1 and the detection resistance r1 of the motor M1 to be measured and returns to the capacitor Ca.

  Next, in step S <b> 6, the convergence determination unit 34 determines whether the ground voltage Vm or the ground current Im detected by the first detection unit 18 has converged. Specifically, the convergence determination unit 34 determines that the ground-to-ground voltage Vm or the ground-to-ground current Im is reduced when the change amount of the waveform of the ground-to-ground voltage Vm or the ground-to-ground current Im detected by the first detection unit 18 is equal to or less than the threshold value TH. Judge that it has converged. The convergence determination unit 34 determines whether the ground voltage Vm or the ground current Im has converged using any one of the first to fourth methods.

  If it is determined in step S6 that the ground voltage Vm or the ground current Im has not converged, it remains in step S6 until it is determined that the ground voltage Vm or the ground current Im has converged, and it is determined that the ground voltage Vm or the ground current Im has converged. Then, the process proceeds to step S7.

  In step S7, the insulation resistance calculation unit 36 determines the measurement target based on the ground voltage Vm or ground current Im detected by the first detection unit 18 and the capacitor voltage Vc detected by the second detection unit 20. The insulation resistance Rm of the motor M1 is calculated. The insulation resistance calculator 36 calculates the insulation resistance Rm based on the ground-to-ground voltage Vm or the ground-to-ground current Im and the capacitor voltage Vc when it is determined that it has converged or after it has been determined that it has converged. To do.

  Next, in step S8, the measurement target selection unit 30 determines whether all the motors M have been selected as measurement targets. That is, the measurement target selection unit 30 determines whether there is a motor M that is not selected as a measurement target. If it is determined in step S8 that all the motors M are not selected as measurement targets, that is, there is a motor M that is not selected as a measurement target, the process returns to step S4.

  If it is determined in step S8 that all the motors M have been selected as measurement targets, the process proceeds to step S9, where the switch control unit 32 turns off the second switch SW2 and all the inverter units 16 (16a to 16c). ) Are all turned off. As a result, the measurement operation ends.

[Modification]
In the above embodiment, one terminal of the capacitor Ca is described as a negative terminal, but one terminal of the capacitor Ca may be a positive terminal. In this case, the positive terminal of the capacitor Ca is connected to the ground via the second switch SW2, and the detection resistor r1 is connected between the positive terminal (one terminal) of the capacitor Ca and the ground. Two switches SW2 are connected in series. Even in this case, the insulation resistance Rm of the motor M can be measured.

[Technical idea obtained from the embodiment]
The technical idea that can be grasped from the above-described embodiments and modifications will be described below.

<First technical idea>
A motor drive device (10) for driving a plurality of motors (M) includes a rectifier circuit (Re) for rectifying an AC voltage supplied from an AC power supply (12) via a first switch (SW1) into a DC voltage; The capacitor (Ca) for smoothing the DC voltage rectified by the rectifier circuit (Re), the positive terminal of the capacitor (Ca) and the motor coil (Cu, Cv, Cw) of the motor (M) are connected. A semiconductor switching element (S) of the arm, a semiconductor switching element (S) of the lower arm that connects the negative terminal of the capacitor (Ca) and the motor coil (Cu, Cv, Cw), By switching operation of the semiconductor switching element (S) and the semiconductor switching element (S) of the lower arm, the capacitor voltage (Vc) of the capacitor (Ca) is converted into an AC voltage and plural A plurality of inverters (16) for driving the motor (M), a second switch (SW2) for connecting one of the positive terminal and the negative terminal of the capacitor (Ca) to the ground, and a capacitor ( A first detector (18) for detecting a ground-to-ground current (Im) or a ground-to-ground voltage (Vm) between one terminal of Ca) and the ground, and a capacitor voltage (Vc) of the capacitor (Ca). The plurality of motors (M) are operated by turning off the upper arm semiconductor switching element (S) and the lower arm semiconductor switching element (S) of each of the second detection unit (20) and the plurality of inverter units (16). Is stopped, the first switch (SW1) is turned off and the second switch (SW2) is turned on, and then the motor coil (Cu, Cv, Cw) of the motor (M) to be measured is connected Of the semiconductor switching element (S) and the lower arm semiconductor switching element (S), the one connected to the other terminal of the capacitor (Ca) is turned on, and the motor coil of the motor (M) other than the measurement target Of the upper-arm semiconductor switching element (S) and the lower-arm semiconductor switching element (S) connected to (Cu, Cv, Cw), the one connected to one terminal of the capacitor (Ca) is turned on. The switch control unit (32) that makes the measurement state in which the insulation resistance (Rm) of the motor (M) to be measured can be measured, and the ground current (1) detected by the first detection unit (18) in the measurement state ( Im) or ground-to-ground voltage (Vm) waveform change amount is calculated, and the ground-to-ground current (Im) or ground-to-ground voltage (Vm) has converged when the change amount is below the threshold (TH). The current-to-ground current (Im) or the voltage-to-ground voltage (Vm) detected by the first detection unit (18) when it is determined that the convergence is determined by the convergence determination unit (34) and the convergence determination unit (34). An insulation resistance calculation unit (36) that calculates an insulation resistance (Rm) of the motor (M) to be measured based on the capacitor voltage (Vc) detected by the second detection unit (20).

  Thereby, the time required for measuring the insulation resistance (Rm) of the motor (M) can be shortened, and the time required for measuring the insulation resistance (Rm) can be prevented from becoming longer than necessary. .

  The convergence determination unit (34) may use the absolute value ΔC of the amount that the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has changed during the predetermined time Δt as the amount of change. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  The convergence determination unit (34) uses ΔC / Δt as the amount of change, where ΔC is the absolute value of the amount of change in the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) during the predetermined time Δt. Also good. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  The convergence determination unit (34) may gradually increase the predetermined time Δt with the passage of time. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  The convergence determination unit (34) may use the absolute value (ΔC) of the differential value (Dv) of the waveform of the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) as the amount of change. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  The convergence determination unit (34) determines that the current has converged when the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) does not change by the reference change amount (ΔCs) even after the predetermined time (T) has elapsed. May be. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

<Second technical idea>
This is a measurement method in which a motor drive device (10) that drives a plurality of motors (M) measures the insulation resistance (Rm) of the motor (M). The motor drive device (10) is rectified by a rectifier circuit (Re) that rectifies an AC voltage supplied from an AC power supply (12) through a first switch (SW1) into a DC voltage, and a rectifier circuit (Re). A capacitor (Ca) for smoothing the DC voltage, and a semiconductor switching element (S) of the upper arm that connects a positive terminal of the capacitor (Ca) and a motor coil (Cu, Cv, Cw) of the motor (M); The lower arm semiconductor switching element (S) for connecting the negative terminal of the capacitor (Ca) and the motor coil (Cu, Cv, Cw), the upper arm semiconductor switching element (S) and the lower arm. The plurality of driving the plurality of motors (M) by converting the capacitor voltage (Vc) of the capacitor (Ca) into an AC voltage by the switching operation of the semiconductor switching element (S). An inverter unit (16), a second switch (SW2) for connecting one of the positive terminal and the negative terminal of the capacitor (Ca) to the ground, one terminal of the capacitor (Ca) and the ground A first detector (18) for detecting a ground-to-ground current (Im) or a ground-to-ground voltage (Vm), a second detector (20) for detecting a capacitor voltage (Vc) of the capacitor (Ca), Is provided. In the measurement method, the upper arm semiconductor switching element (S) and the lower arm semiconductor switching element (S) of each of the plurality of inverter units (16) are turned off to stop the operation of the plurality of motors (M). After turning the first switch (SW1) off and the second switch (SW2) on, the upper arm semiconductor switching element (S) to which the motor coil (Cu, Cv, Cw) of the motor (M) to be measured is connected ) And the lower arm semiconductor switching element (S), the one connected to the other terminal of the capacitor (Ca) is turned on, and the motor coils (Cu, Cv, Cw) is connected to one terminal of the capacitor (Ca) of the upper arm semiconductor switching element (S) and the lower arm semiconductor switching element (S). The first detection unit (18) detects the switch control step in which the connected one is turned on and the measurement state allows the measurement of the insulation resistance (Rm) of the motor (M) to be measured, and the measurement state. The amount of change in the waveform of the ground-to-ground current (Im) or ground-to-ground voltage (Vm) is calculated, and when the amount of change falls below the threshold (TH), the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) A convergence determination step for determining convergence and a current to ground (Im) or a voltage to ground (Vm) detected by the first detection unit (18) and second detection when it is determined that the convergence has been determined by the convergence determination step. An insulation resistance calculation step of calculating an insulation resistance (Rm) of the motor (M) to be measured based on the capacitor voltage (Vc) detected by the unit (20).

  Thereby, the time required for measuring the insulation resistance (Rm) of the motor (M) can be shortened, and the time required for measuring the insulation resistance (Rm) can be prevented from becoming longer than necessary. .

  In the convergence determination step, the absolute value ΔC of the amount by which the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has changed during the predetermined time Δt may be used as the amount of change. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  In the convergence determination step, ΔC / Δt may be used as the amount of change, where ΔC is an absolute value of the amount of change in the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) during the predetermined time Δt. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  In the convergence determination step, the predetermined time Δt may be gradually increased as time passes. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  In the convergence determination step, the absolute value (ΔC) of the differential value (Dv) of the waveform of the current to ground (Im) or the voltage to ground (Vm) may be used as the amount of change. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

  In the convergence determination step, even if the predetermined time (T) elapses, if the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) does not change by the reference change amount (ΔCs), it is determined that the current has converged. Good. Thereby, it is possible to accurately determine whether or not the ground-to-ground current (Im) or the ground-to-ground voltage (Vm) has converged.

DESCRIPTION OF SYMBOLS 10 ... Motor drive device 12 ... AC power supply 14 ... Converter part 16 (16a-16c) ... Inverter part 18 ... 1st detection part 20 ... 2nd detection part 22 ... Control part 30 ... Measuring object selection part 32 ... Switch control part 34 ... Convergence determining unit 36 ... Insulation resistance calculating unit Ca ... Capacitors Cu, Cv, Cw ... Motor coil Im ... Current to ground M (M1-M3) ... Motor r1, r2 ... Detection resistor Re ... Rectifier circuit Rm (Rm1-Rm3) ... Insulation resistance S (Suu, Svu, Swu, Sud, Svd, Swd) ... Semiconductor switching element SW1 ... First switch SW2 ... Second switch Vm ... Ground voltage

Claims (4)

A motor drive device for driving a plurality of motors,
A rectifier circuit that rectifies an AC voltage supplied from an AC power supply via a first switch into a DC voltage;
A capacitor for smoothing the DC voltage rectified by the rectifier circuit;
An upper arm semiconductor switching element for connecting the positive terminal of the capacitor and the motor coil of the motor; and a lower arm semiconductor switching element for connecting the negative terminal of the capacitor and the motor coil. A plurality of inverter units for driving a plurality of motors by converting a capacitor voltage of the capacitor into an AC voltage by a switching operation of the semiconductor switching element of the upper arm and the semiconductor switching element of the lower arm;
A second switch for connecting one of the positive terminal and the negative terminal of the capacitor to the ground;
A first detector for detecting a ground-to-ground current or a ground-to-ground voltage between the one terminal of the capacitor and the ground;
A second detector for detecting the capacitor voltage of the capacitor;
The upper arm semiconductor switching element and the lower arm semiconductor switching element of each of the plurality of inverter units are turned off to stop the operation of the plurality of motors, the first switch is turned off, and the second switch is turned on. Then, the upper arm semiconductor switching element to which the motor coil of the motor to be measured is connected and the lower arm semiconductor switching element connected to the other terminal of the capacitor are turned on. The upper arm semiconductor switching element and the lower arm semiconductor switching element to which the motor coil of the motor other than the measurement target is connected are connected to the one terminal of the capacitor. Is turned on and the insulation resistance of the motor to be measured is measured. A switch control unit for the measurement state that,
In the measurement state, the amount of change in the waveform of the ground-to-ground current or the ground-to-ground voltage detected by the first detection unit is calculated, and the ground-to-ground current or the ground-to-ground when the amount of change falls below a threshold value A convergence determination unit that determines that the voltage has converged;
When the convergence determining unit determines that the convergence has occurred, the measurement is performed based on the ground current or the ground voltage detected by the first detection unit and the capacitor voltage detected by the second detection unit. An insulation resistance calculator that calculates the insulation resistance of the target motor;
Equipped with a,
The convergence determination unit uses the absolute value ΔC of the amount of change in the ground-to-ground current or the ground-to-ground voltage during the predetermined time Δt as the amount of change, and gradually increases the predetermined time Δt as time elapses. Motor drive device. A motor drive device for driving a plurality of motors,
A rectifier circuit that rectifies an AC voltage supplied from an AC power supply via a first switch into a DC voltage;
A capacitor for smoothing the DC voltage rectified by the rectifier circuit;
An upper arm semiconductor switching element for connecting the positive terminal of the capacitor and the motor coil of the motor; and a lower arm semiconductor switching element for connecting the negative terminal of the capacitor and the motor coil. A plurality of inverter units for driving a plurality of motors by converting a capacitor voltage of the capacitor into an AC voltage by a switching operation of the semiconductor switching element of the upper arm and the semiconductor switching element of the lower arm;
A second switch for connecting one of the positive terminal and the negative terminal of the capacitor to the ground;
A first detector for detecting a ground-to-ground current or a ground-to-ground voltage between the one terminal of the capacitor and the ground;
A second detector for detecting the capacitor voltage of the capacitor;
The upper arm semiconductor switching element and the lower arm semiconductor switching element of each of the plurality of inverter units are turned off to stop the operation of the plurality of motors, the first switch is turned off, and the second switch is turned on. Then, the upper arm semiconductor switching element to which the motor coil of the motor to be measured is connected and the lower arm semiconductor switching element connected to the other terminal of the capacitor are turned on. The upper arm semiconductor switching element and the lower arm semiconductor switching element to which the motor coil of the motor other than the measurement target is connected are connected to the one terminal of the capacitor. Is turned on and the insulation resistance of the motor to be measured is measured. A switch control unit for the measurement state that,
In the measurement state, the amount of change in the waveform of the ground-to-ground current or the ground-to-ground voltage detected by the first detection unit is calculated, and the ground-to-ground current or the ground-to-ground when the amount of change falls below a threshold value A convergence determination unit that determines that the voltage has converged;
When the convergence determining unit determines that the convergence has occurred, the measurement is performed based on the ground current or the ground voltage detected by the first detection unit and the capacitor voltage detected by the second detection unit. An insulation resistance calculator that calculates the insulation resistance of the target motor;
With
The convergence determination unit sets ΔC / Δt as the amount of change when ΔC is an absolute value of the amount of change in the ground-to-ground current or the ground-to-ground voltage during a predetermined time Δt, and the predetermined time Δt A motor drive device that gradually increases the length of the motor over time . A motor driving device for driving a plurality of motors is a measuring method for measuring the insulation resistance of the motor,
The motor driving device is
A rectifier circuit that rectifies an AC voltage supplied from an AC power supply via a first switch into a DC voltage;
A capacitor for smoothing the DC voltage rectified by the rectifier circuit;
An upper arm semiconductor switching element for connecting the positive terminal of the capacitor and the motor coil of the motor; and a lower arm semiconductor switching element for connecting the negative terminal of the capacitor and the motor coil. A plurality of inverter units for driving a plurality of motors by converting a capacitor voltage of the capacitor into an AC voltage by a switching operation of the semiconductor switching element of the upper arm and the semiconductor switching element of the lower arm;
A second switch for connecting one of the positive terminal and the negative terminal of the capacitor to the ground;
A first detector for detecting a ground-to-ground current or a ground-to-ground voltage between the one terminal of the capacitor and the ground;
A second detector for detecting the capacitor voltage of the capacitor;
With
The upper arm semiconductor switching element and the lower arm semiconductor switching element of each of the plurality of inverter units are turned off to stop the operation of the plurality of motors, the first switch is turned off, and the second switch is turned on. Then, the upper arm semiconductor switching element to which the motor coil of the motor to be measured is connected and the lower arm semiconductor switching element connected to the other terminal of the capacitor are turned on. The upper arm semiconductor switching element and the lower arm semiconductor switching element to which the motor coil of the motor other than the measurement target is connected are connected to the one terminal of the capacitor. Is turned on to measure the insulation resistance of the motor to be measured. A switch control step of the measurement ready,
In the measurement state, the amount of change in the waveform of the ground-to-ground current or the ground-to-ground voltage detected by the first detection unit is calculated, and the ground-to-ground current or the ground-to-ground when the amount of change falls below a threshold value A convergence determining step for determining that the voltage has converged;
Based on the current to ground or the voltage to ground detected by the first detection unit and the capacitor voltage detected by the second detection unit when it is determined that the convergence has been made by the convergence determination step. An insulation resistance calculating step for calculating the insulation resistance of the target motor;
Only including,
The convergence determination step uses the absolute value ΔC of the amount of change in the ground-to-ground current or the ground-to-ground voltage during the predetermined time Δt as the amount of change, and gradually increases the predetermined time Δt over time. ,Measuring method. A motor driving device for driving a plurality of motors is a measuring method for measuring the insulation resistance of the motor,
The motor driving device is
A rectifier circuit that rectifies an AC voltage supplied from an AC power supply via a first switch into a DC voltage;
A capacitor for smoothing the DC voltage rectified by the rectifier circuit;
An upper arm semiconductor switching element for connecting the positive terminal of the capacitor and the motor coil of the motor; and a lower arm semiconductor switching element for connecting the negative terminal of the capacitor and the motor coil. A plurality of inverter units for driving a plurality of motors by converting a capacitor voltage of the capacitor into an AC voltage by a switching operation of the semiconductor switching element of the upper arm and the semiconductor switching element of the lower arm;
A second switch for connecting one of the positive terminal and the negative terminal of the capacitor to the ground;
A first detector for detecting a ground-to-ground current or a ground-to-ground voltage between the one terminal of the capacitor and the ground;
A second detector for detecting the capacitor voltage of the capacitor;
With
The upper arm semiconductor switching element and the lower arm semiconductor switching element of each of the plurality of inverter units are turned off to stop the operation of the plurality of motors, the first switch is turned off, and the second switch is turned on. Then, the upper arm semiconductor switching element to which the motor coil of the motor to be measured is connected and the lower arm semiconductor switching element connected to the other terminal of the capacitor are turned on. The upper arm semiconductor switching element and the lower arm semiconductor switching element to which the motor coil of the motor other than the measurement target is connected are connected to the one terminal of the capacitor. Is turned on to measure the insulation resistance of the motor to be measured. A switch control step of the measurement ready,
In the measurement state, the amount of change in the waveform of the ground-to-ground current or the ground-to-ground voltage detected by the first detection unit is calculated, and the ground-to-ground current or the ground-to-ground when the amount of change falls below a threshold value A convergence determining step for determining that the voltage has converged;
Based on the current to ground or the voltage to ground detected by the first detection unit and the capacitor voltage detected by the second detection unit when it is determined that the convergence has been made by the convergence determination step. An insulation resistance calculating step for calculating the insulation resistance of the target motor;
Including
In the convergence determination step, when the absolute value of the amount of change in the ground-to-ground current or the ground-to-ground voltage during a predetermined time Δt is ΔC, ΔC / Δt is the amount of change , and the predetermined time Δt A measurement method that gradually increases the length over time .

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